Interactions Flashcards
What are the interactions of methotrexate?
Can cause blood disorders, photosensitivity, respiratory effects
Trimethoprim: both anti-folate drugs - increased risk of haematological side effects + risk of nephrotoxicity
NSAIDs: increased risk of toxicity + nephrotoxicity
Penicillins: increased risk of toxicity
Aspirin: increased risk of toxicity + nephrotoxicity
Co-trimoxazole: sulfamethoxazole increases exposure to methotrexate and trimethoprim increases haematological side effects
Omeprazole: decreases clearance of methotrexate (lansoprazole is a better option)
Quinolones: increases toxicity
What are the interactions of statins?
Macrolides
Grapefruit jucie
Fusidic acid (oral only) - wait for 7 days before going back to statins
Colchicine
Fluconazole
Amlodipine with simvastatin over 20mg
What are the interactions for warfarin?
Amiodarone
Cranberry and pomegranate juice
Azoles (topical + oral)
Omeprazole
Alcohol
NSAIDs
Ciprolfoxacin
What are common interactions of theophyline?
Serum conc target: 10-20mg/L
Toxicity - activated charcoal
Tobacco (potent enzyme inducer)
Diuretics
Rifampicin
Erythromycin
Cimetidine
Phenytoin
Ciprofloxacin
What are the interactions of omeprazole?
Only PPI that can be taken in pregnancy
PPIs can mask gastric cancer symptoms
Increase risk of lupus
Cause gastric infections e.g. C.diff
Hypomagnesaemia
Osteoporosis
Warfarin
Methotrexate
Escitalopram
Clopidogrel: omeprazole reduces anti-platelet effect of clopidogrel
Citalopram
What are the interactions of sildenafil?
Do not supply to patient who had stroke in last 6 months
Alpha blockers
Erythromycin
Nitrates
Diltiazem
Ritonavir
Nicorandil
What are the interactions of amiodarone?
Can cause corneal micro-deposits
Digoxin
Verapamil
Diltiazem
Grapefruit juice
Flecanide
Warfarin
Phenytoin
What are the interactions of St John’s Wort?
Aminophyline
Phenytoin
Contraceptives
Vinca alkaloids
Warfarin
Theophyline
Statins
What is the interaction between allopurinol and azathioprine?
Allopurinol increases risk of haematological toxicity - adjust azathioprine dose to just one quarter of regular dose
What should be avoided with MR and gastro-resistant mesalazine?
Lactulose - lowers stool pH in intestine = prevents sufficient release
What should be avoided with co-danthramer?
Bulk-forming laxatives - causes painful colic and obstruction
What is the interaction between theophylline and beta2-agonists?
Potentially serious hypokalaemia - particular caution in severe asthma
What decreases theophylline concentration?
Smoking
Alcohol
Enzyme inducers
Which drugs increase the risk of hypokalaemia with theophylline?
Corticosteroids
Loop and thiazide diuretics
Beta-2 agonists
What drug increases the risk of convulsions with theophylline?
Ciprofloxacin (quinolones) - an enzyme inhibitor and lowers seizure threshold
A side effect of theophylline is also convulsions
What drugs increase the plasma concentration of theophylline?
CCB
Cimetidine
Fluconazole
Macrolides
What drugs reduce the plasma concentrations of theophylline?
St Johns Wort
Rifampicin
Phenytoin
Carbamazepine
Phenobarbital
What is the interaction between methotrexate and aminophylline?
Methotrexate decreases clearance of aminophylline
Which anti-epileptics reduce clearance of methotrexate?
Levetiracetam, phenytoin and sodium valproate
They also increase the risk of liver toxicity
What is the interaction between methotrexate and NSAIDs
Increased risk of renal toxicity = risk of methotrexate toxicity
What is the interaction between methotrexate and fluconazole?
Increases risk of liver toxicity
What is the interaction between methotrexate and isotretinoin?
Increased risk of liver toxicity
What is the interaction between methotrexate and penicillins?
Reduced clearance of methotrexate (if short course up to 10 days - consider using and monitor for signs of methotrexate toxicity)
What is the interaction between methotrexate and PPIs?
Reduced methotrexate clearance - consider H2-receptor antagonists as alternative
What is the interaction between methotrexate and statins?
Increased risk of liver toxicity
What is the interaction between methotrexate and tamoxifen?
Increased risk of liver toxicity
What is the interaction between methotrexate and terbinafine?
Increased risk of liver toxicity
What juice decreases ciclosporin concentration?
Purple grape juice
What is the interaction between an SSRI and NSAIDs
GI bleed
What is the interaction between Ibuprofen and ramipril
Nephrotoxicity
What is the interaction between simvastatin and amlodipine
myopathy
What is the interaction between ramipril and spironolactone
Hyperkalaemia
What is the interaction between bisoprolol and donepezil?
Bradycardia
What would cause a pharmacodyamic interaction with donepezil?
Oxybutynin - anticholinergic drugs counteract what this does because donepezil prevents the breakdown of acetylcholinterase in the brain whereas anticholingeric drugs does the opposite
What is the interaction between sodium valproate and doxycycline?
Risk of hepatotoxicity
Do SSRIs impact epilepsy?
SSRIs lower seizure threshold
What is the interaction between sildenafil and nitrates?
CONTRAINDICATED - risk of hypotension
What is the interaction between alpha blockers and sildenafil?
Risk of hypotension
What is the interaction between ACEi and insulin or other oral antidiabetics?
Hypoglycaemia
What is the interaction between lithium and candesartan?
Candesartan increases concentration of lithium
What do MAOIs interact with?
Tyramine: the cheese effect - hypertensive crisis
Sympathomimetics: pseudoephedrine, epherdrine - hypertensive crisis
Sumatriptan: increases exposure to sumatriptan - avoid for 14 days after stopping MAOI
Other antidepressants: washout period
Lithium: increased risk of serotonin syndrome
